Method for forming an article having a decorative surface

ABSTRACT

The invention refers to a method for forming an article having a decorative surface comprising: a) screen printing an ink composition comprising a curable composition onto at least one major surface of a thermoformable polymeric sheet; b) curing said curable composition to obtain a printed sheet having on at least one major surface an ink comprising a cured composition; and c) thermoforming the printed sheet to obtain a decorated article, wherein said curable composition comprises a polyisocyanate and a component comprising isocyanate reactive groups and wherein said ink composition contains a solvent or solvent blend in which said curable composition is soluble or miscible.

INVENTION FIELD

The present invention relates to a method for forming an article havinga decorative surface using thermoforming.

The method of the present invention may find application in a variety ofindustries involving articles having a decorative surface. The method isparticularly, but not exclusively, suitable for application in theautomotive industry, including articles for all type of vehicles, i.e.cars, motorbikes, trucks, wherein tri-dimensional external decoratedarticles are desired. Decorated articles that can be produced with themethod can be used in interior applications as well as in exteriorapplications where the decorated article is exposed to varying weatherconditions of, for example, temperature, sunshine, humidity, etc. . . ..

BACKGROUND

Methods for forming articles having decorative surfaces have beenalready described in the past. Within the last few years, a newdecoration technique known as in-mold decoration (IMD) has gainedacceptance and use in the molding industry and solves several of theproblems associated with prior art techniques. See for example U.S. Pat.Nos. 4,059,471; 4,650,533; 4,356,230 and 4,202,663. IMD combines theprocess of forming an article by injection molding with decoration ofthe article. In this method, a plastics carrier sheet, bearing a printedimage, is placed in the cavity of an injection molding tool. Moltenthermoplastic resin is then injected into the cavity to contact thecarrier sheet. With suitable design of the injection molding tool, thepre-printed plastics carrier sheet becomes integral to the moldedarticle or part. This is contrasted with the process described, forexample, in European Patent application No. 799,681, where an image istransferred onto an article during the injection molding process. Themolding process therein disclosed is a reaction injection molding,whereby reactive polymer components are injected into a mold at arelatively low temperature. The reactive components are mixed byinjection and undergo a reaction, which raises the temperature of themixture in the mold and produces hardened, cross-linked polymers.

The injection molding technique allows obtaining good results in termsof quality and precision also in case of decoration of articles having acomplex shape. However, it has the disadvantage that it is verydifficult and expensive to make modifications to the molds or anypersonalization to the printing process.

Another technique known in the art is the so-called thermoformingprocess, disclosed, for example, in the International Application No.2004/067,599. It discloses flexible radiation curable compositionsuseful in thermoforming process which includes the steps of: 1) screenprinting a polymeric sheet with a graphic design; 2) UV curing theprinted ink; 3) thermoforming the printed sheets; 4) pressing thethermoformed sheet into a mold and applying vacuum; 5) cooling theproduct and removing it from the mold; 6) finishing the product to giveit the final desired shape. The method therein described has theadvantages to allow the ink to show good adhesion to the polymericsheet, to avoid that prints stacked on top of each other stick to eachother, to give the ink excellent flexibility and to allow successiveinterventions for aesthetical modification in the printing process.However, the decorated surface of the final product obtained by themethod therein described has the disadvantage to show unpleasing cracksin the ink printed sheet, which aesthetically decrease its appearancefor three-dimensional articles that include sharp angles. Additionally,the articles produced with the method disclosed in this internationalapplication, typically do not allow usage in exterior applications andin particular these articles do not satisfy stringent requirements thatare imposed in the automotive industry.

INVENTION DESCRIPTION

The present invention can provide a method by which three-dimensionaldecorative articles can be produced in a cost effective and convenientway. The present method can also allow three-dimensional decorativearticles to be formed that include sharp angles (e.g., angles ofapproximately 90 degrees, angles of less than 90, 85, 80, 75, 70, 65,60, 55, 50 or 45 degrees, or even smaller angles) without the visible(i.e., with normal unaided human eyesight) appearance of cracking in thedecorative design. In addition, the present method can allowthree-dimensional decorative articles to be formed that result in thedecorative design printed on the article from being substantiallyelongated (e.g., up to a percent elongation of 120%, 140%, 160%, 180% oreven greater) without the visible (i.e., with normal unaided humaneyesight) appearance of cracking in the decorative design. Furthermore,the present method can be employed in the production of articlessuitable for use in exterior applications and capable of fulfilling theperformance and aesthetic requirements that are typical in theautomotive industry.

In one aspect, the invention relates to a method for forming an articlehaving a decorative surface comprising:

a) screen printing an ink composition comprising a curable compositiononto at least one major surface of a thermoformable polymeric sheet;

b) curing said curable composition to obtain a printed sheet having onat least one major surface an ink comprising a cured composition; and

c) thermoforming the printed sheet to obtain a decorated article,

wherein the curable composition comprises a polyisocyanate and acomponent comprising isocyanate reactive groups and wherein said inkcomposition contains a solvent or solvent blend in which said curablecomposition is soluble or miscible.

The article used in the method of the invention can be any articlehaving a decorative surface used in the motor bike or automotiveindustry, in particular used as external articles, such as, for example,side or front mounted rearview mirror covers or housings, pillars,motorbike gas tank covers, head lamps, sunroofs, windows supports, orsimilar. The article can also be used in portions of the interior of,for example, a motor vehicle or other vehicle. Such vehicle interiorportions can include, for example, parts of the instrumental panels,door traps or interior door trims, video display moldings, etc.

An advantage associated with the method of the present invention is thatthe article obtained with said method generally does not result inundesired visible cracks in the decorative design on the surface of thearticle, even if the decorative article has complex parts, shapes and/orsharp angles. The decorative articles also maintain the good propertiesof flexibility and adhesion of the decorative design to the polymericsheet. Still further, the resulting decorative articles typically areuseful in exterior application and fulfill the needs for automotiveapplications.

According to a particular embodiment of the present invention, it isbelieved that the ink composition can be allowed to partially penetrateinto the thermoformable polymeric sheet, thereby improving the adhesionof the printed ink to the thermoformable sheet.

Screen printing is essentially a stencil printing process which may nowbe generated by computer with the aid of various software packages. Itsability to vary and control ink thickness accurately has made it anextremely useful process for the decoration of many different types ofplastic substrates.

In screen printing, as disclosed for example in U.S. Pat. No. 6,465,102,a screen or stencil is prepared and bonded to a fine weave fabric whichis then tensioned in a rigid frame. The basic screen-printing processinvolves, for example, the use of a flat bed where generally thesubstrate is held by vacuum during printing.

The screen printing step a) of the method may be repeated one or moretimes as needed, one for each color, depending on the number of desiredcolor combinations to be printed on the decorated surface of the finalarticle to obtain a desired full color decorated surface. It can bedesirable to limit the number of times the screen printing step a) ofthe method is repeated, where the printed images at least overlap one ontop of the other, in order to avoid interlayer adhesion problemsresulting from image stacks that are too thick. It may be desirable tolimit such printed image stacks to 5 or 6 layers (i.e., 5 or 6 printingsteps) for the same decorative article.

Thermoformable polymeric sheets useful for receiving ink during thescreen printing step a) according to the method of the present inventionmay be selected from conventional thermoplastic polymer material suchas, for example, polycarbonate, polyesters, polyacrylates, polystyrene,polyethyleneterephthalate glycol (PETG), acrylonitrile butadiene styrene(ABS), thermoplastic polyolefin (TPO), polypropylene, acrylic compounds,and mixtures thereof. Due to superior mechanical and thermal properties,polycarbonate is preferred in the manufacturing of numerous part andcomponents in the automotive industry. However, any other suitablethermoformable polymeric sheet may be used. The substrate may be asingle layer structure or a multilayered structure.

The ink composition to be printed onto the thermoformable polymericsheet during the screen printing step a) according to the method of thepresent invention contains at least a curable composition and a solventor solvent blend in which the curable composition is soluble.

The curable composition comprises a polyisocyanate and a compound havingisocyanate reactive groups. Suitable isocyanate reactive groups includehydroxyl groups and amino groups. In one embodiment of the invention,the compound having isocyanate reactive groups is a polymeric compound(e.g., a polymeric polyol). Generally, the compound having isocyanatereactive groups comprises at least two, generally at least threeisocyanate reactive groups. Examples of compounds having isocyanatereactive groups include polyols, in particular acrylic or methacrylichomo- or copolymers having hydroxyl groups, for example having at leastthree hydroxyl groups. Further suitable isocyanate reactive compoundsinclude polyolefins having isocyanate reactive groups, polyesters havingisocyanate groups, polyurethanes having isocyanate reactive groups etc.. . . . In a particular embodiment in connection with the presentinvention, the curable composition includes a caprolactone orcaprolactone polyol (i.e., polycaprolactone) having isocyanate reactivegroups, in particular having two or three hydroxy groups. Moreparticularly, the curable composition can include a polyester polyol,derived from caprolactone monomer, terminated by primary hydroxylgroups. The molecular weight of the isocyanate reactive compound mayvary widely and can be between 500 g/mol and 500,000 g/mol, for examplebetween 1000 g/mol and 100,000 g/mol or between 10,000 g/mol and 80,000g/mol. Simple low molecular weight compounds may be used as well such asfor example alkane diols and alkane triols such as for example glycerol,butane diol and the like. The properties of the ink composition can betailored by altering the molecular weight and/or the functionality ofthe curable composition.

The total amount of isocyanate reactive compounds in the ink compositionis typically between 1 and 20% by weight based on the total amount ofsolids in the ink composition. A typical amount is generally between 2and 15% by weight or between 3 and 10% by weight. Generally, the higherthe amount of isocyanate reactive compounds for the same ratio ofisocyanate to isocyanate reactive compounds, the less flexible theresulting cured ink may become, although the kind and nature of thepolyisocyanate and isocyanate reactive compounds may influence theresulting flexibility as well.

The polyisocyanate used in the curable composition can aliphatic oraromatic. Generally the polyisocyanate compound is a di-isocyanate ortri-isocyanate. Polymeric or oligomeric isocyanate containing compoundsmay be used as well.

Mixtures of different polyisocyanate compounds can be used as well. Whena mixture of polyisocyanate compounds is used, the average amount ofisocyanate groups per molecule will be more than 2 for example at least2.2 or at least 2.5. Specific examples include toluene-diisocyanate,toluene-triisocyanate, 2,6-toluene diisocyanate, diphenylmethanediisocyanate, isophorone-diisocyanate, hexamethylene diisocyanate,xylene diisocyanate, among others. The amount of polyisocyanatecompounds in the curable composition is typically such that at least astoichiometric amount and preferably an excess of isocyanate groups toisocyanate reactive groups in the composition is present. However it isalso possible to use less than a stoichiometric amount.

The ink composition generally will further include a synthetic resin(generally not containing an isocyanate reactive group) such as, forexample only, polyester-based resins, polycarbonate-based resins,polyvinyl chloride-based resins, acrylic-based resins, polycaprolactonesor similar. Mixtures of synthetic resins can be advantageously employed.The ink composition will generally also include dyes or pigments toobtain an ink having a desired color.

In a particular aspect of the invention, the ink composition may containmetallic pigments and/or mica. In a particular embodiment, the inkcomposition comprises a lactone or polylactone compound that may or maynot have isocyanate reactive groups. The lactone or polylactonecompounds suitable for use in accordance with the present inventionadvantageously has from about 3 to about 20 carbon atoms. Examples ofsuitable lactones include caprolactone, t-butyl caprolactone,zeta-enantholactone; delta-valerolactones;monoalkyl-delta-valerolactones, such as the monomethyl-, monoethyl-, andmonohexyl-delta-valerolactones, and the like; monoalkyl, dialkyl, andtrialkyl-epsilon-caprolactones such as the monomethyl-, monoethyl-,monohexyl-, dimethyl-, di-n-hexyl, trimethyl-,triethyl-epsilon-caprolactones, 5-nonyl-oxepan-2-one, 4,4,6- or4,6,6-trimethyl-oxepan-2-one and the like; 5-hydroxymethyl-oxepan-2-one;beta-lactones, for example, beta-propiolactone; beta-butyrolactone orpivalolactone; gamma-lactones, such as gamma-butyrolactone; dilactones,such as lactide; dilactides; glycolides, such as tetramethyl glycolides,and the like; dioxanones, such as 1,4-dioxan-2-one, 1,5-dioxepan-2-one,and the like. The lactones can be the optically pure isomers or two ormore optically different isomers or other mixtures. Epsilon-caprolactoneand its derivatives, for example, methyl-epsilon-caprolactone, and otherseven membered ring lactones are especially preferred.

Suitable solvents or solvent blends for use with the ink compositioninclude those selected from ketones, such as, for example,cyclohexanone, isophorone, diacetone alcohol, acetophenone, di-isobutylketone; esters, such as for example, methoxypropyl acetate,isopropoxyethyl acetate, diethylene glycol ethyl ether acetate, ethyleneglycol butyl ether acetate, ethoxyethyl propionate, ethyl lactate,isopropoxyethyl acetate, ethoxypropyl acetate, dimethyl succinate,dimethyl glutarate, dimethyl adipate, butoxyethyl acetate; and amides,such as for example, N-methylpyrrolidone. A mixture of these solventsmay also be used.

In a particular embodiment, the solvent used is cyclohexanone. Inparticular, it is believed that the use of cyclohexanone as a solventand the use of the polycarbonate as thermoformable polymeric sheet hasthe advantage to greatly improve the penetration into the thermoformablepolymeric sheet of the ink material containing the ink composition andthe solvent in which the ink composition is soluble. Specific examplesof polycarbonate materials that can be used for the thermoformablepolymeric sheet include, but are not limited to: Makrofol® polycarbonatesheets, available from Bayer AG (Darmstadt, Germany). It can beparticularly desirable (e.g., for Automotive applications) to usepolycarbonate or other thermoformable polymeric sheets that have beenadapted to be resistant against degradation caused by ultraviolet (UV)radiation such as, for example, Makrofol® TP244, Makrofol® 1099UV or GELexan SLX. When the thermoformable polymeric sheet is transparent andthe ink image is printed on the backside of the polymeric sheet, the topsurface (i.e., opposite to the printed ink) can be UV protected.Protecting against UV radiation can significantly improve the durabilityof the printed ink image and the thermoformable plastic sheet.

The following components may also be added to the ink composition:matting agents, surfactants, stabilizers, plasticizers, extenders,biocides, and similar.

The total amount of solids in the ink composition may vary widely but isgenerally between 15% by weight and 60% by weight, for example between20% by weight and 45% by weight or between 22 and 40% by weight.

The ink composition is screen-printed on one or both major sides of thethermoformable sheet. In one particular embodiment the ink compositionis screen printed on the back side of the thermoformable sheet, i.e. theside opposite to the side that will define the exterior surface of thedecorative article. In such a case, if the decoration involves an image,the image would be printed in reverse. In an alternative embodiment, theink composition is printed on the side that forms the exterior surfaceof the decorative article and the image would thus be exposed on thesurface of the decorative article. In such a case, it will generally beadvantage to apply a clear coat on top of printed ink layer(s). Such aclear coat would serve as a protective layer (e.g., to provide abrasionresistance) and would typically be based on a curable composition, forexample similar to the curable composition included in the inkcomposition. Generally, the clear coat may be applied by screen printingas well, for example as a final printing after all ink layers have beenprinted. The clear coat may also be provided as a continuous layeroverlaying printed as well as non-printed layers. According to yet afurther embodiment, the ink composition is printed on both sides of thethermoformable sheet. This allows for obtaining special graphicaleffects that may desired in a particular application such as, forexample, an image or graphic including glossy printing overlaid withmatte printing designs.

The curing step b), according to the method of the present invention,typically involves a cross-linking reaction of the polyisocyanate andthe compound having isocyanate reactive groups. Typically, the curing isheat activated, for example, by irradiation of the printed sheet withinfrared light A catalyst for accelerating the curing of the curablecomposition may also be used in the ink composition such that lessenergy will be required to activate the cross-linking reaction.

Typically, the curing step involves heat activation to a temperature ofup to 90° C., up to 120° C. or even more, depending on the materialschosen. It can be desirable for the curing step to involve heatactivation to a temperature of, for example, from 30° C. to 80° C. orfrom 40° C. to 60° C. Varying temperature profiles may be used to causecuring. Also, generally heat activation should proceed for a timesufficient to obtain a desired level of curing such that a subsequentcolor can be printed without blending the different colors together.Depending on the ink composition, this time can be between for example0.5 and 5 minutes. Further, subsequent of the printing of the differentcolors, a further heat activation may be employed to fully cure thecurable composition in the ink composition(s). Generally, this furtherheat activation will take at least 30 minutes, for example at least onehour and may be up to several hours. A full cure may also take severaldays (e.g., 3 days). Also, a higher temperature may be used in thisfurther heat activation and curing.

Then, the printed and cured sheets are optionally stacked andtransported to another location for being subjected to the thermoformingstep c).

The thermoforming step c) is generally performed by inserting the inkprinted sheets into a thermoforming machine and then heating them byinfrared or other radiant heat source to soften the polymeric sheet,with the temperature and time of the heating operation dependent uponthe type of thermoforming polymeric sheet.

The ink printed sheets are inserted in the thermoforming machine andtherein maintained in a fixed position, for example by clamping them, inorder to allow a uniform thermoforming step.

When the sheet is sufficiently soft, a mold may be pressed into theprinted side (or optionally into the unprinted side) of the sheet and,due to the flexibility that the sheet is obtained in consequence of thethermoforming step, the sheet is allowed to tightly wrap the mold form,taking on its shape permanently. In a particular embodiment, the sheetis pressed between a male and female component of a mold. Vacuum isgenerally applied to allow the sheet to better wrap the mold.

After the sheet has obtained its shape, cooling air is convenientlyapplied to harden the sheet and to allow it to reach a solid shape.

The thermoformed sheet is then removed from the thermoforming machineand subjected to the final finishing step by cutting it, for example bya die-cutting device, to give it the final shape.

The finished decorated article exhibited good scratch resistance, andmaintain excellent adhesion to the polymeric sheet.

The finishing step of the method of the present invention may furtherinclude the step of applying a transparent coat to the decorativesurface as a protective layer as disclosed above.

The invention is further illustrated with reference to the followingexamples without the intention however to limit the invention thereto.

EXAMPLES Materials for the Ink Composition Examples 1 and 2

D7900: Clear base ink for preparing desired colored inks commerciallyavailable from 3M Company. The clear base ink is based on a PVC resinand acrylic resin and containing a solvent mixture of cyclohexanone,aromatic solvents and ethylene glycol butyl ether acetate.

P1 and P2: pigment dispersions commercially available from 3M Companyand suitable for blending with D7900.

Joncryl™ 587: acrylic polyol commercially available from Johnson(Johnson Polymer LLC, Sturtevant, Wis. 53177-0902, US).

TONE™ 200: polycaprolactone diol commercially available from Dow (Dow,Midland, Mich. 48674, US).

HEMI: hexamethylene di-isocyanate, Desmodur™ N 3390 BA/SN, commerciallyavailable from Bayer (Bayer Material Science AG, 51368 Leverkusen,Germany).

CGS 80: thinner commercially available from 3M Company

The ink composition of Example 1, according to the invention, wasprepared having the following composition:

-   -   a) 50 parts per weight D 7900;    -   b) 40 parts per weight of a pigment dispersion P1;    -   c) 0.87 parts by weight Joncryl™ 587;    -   d) 0.43 parts by weight of TONE™ 200;    -   e) 0.0002 parts by weight dibutyltindilaurate;    -   f) 1.8 parts by weight HMDI;    -   g) 5.7 parts by weight CGS 80.

The ink composition of Example 2, according to the invention, wasprepared similar as the ink composition of Example 1 but using pigmentdispersion P2 to achieve a differently colored ink.

Materials for the Ink Composition of Examples 3 and 4

D7900: Clear base ink for preparing desired colored inks commerciallyavailable from 3M Company. The clear base ink is based on a PVC resinand acrylic resin and containing a solvent mixture of cyclohexanone,aromatic solvents and ethylene glycol butyl ether acetate.

P1 and P2: pigment dispersions commercially available from Kiian S.p.a.Luisago, Italy with trade name Mankounian-Argon Thermoplus 49000 seriesand intended for blending with D7900 clear resin.

Joncryl™ 587: acrylic polyol commercially available from Johnson(Johnson Polymer LLC, Sturtevant, Wis. 53177-0902, US).

TONE™ 200: polycaprolactone diol commercially available from Dow (Dow,Midland, Mich. 48674, US).

HMDI: hexamethylene di-isocyanate, Desmodur™ N 3390 BA/SN, commerciallyavailable from Bayer (Bayer Material Science AG, 51368 Leverkusen,Germany).

Desmophen A450M PA/X: acrylic polyol available from Bayer (BayerMaterial Science AG, 51368 Leverkusen, Germany).

CGS 80: thinner commercially available from 3M Company.

The ink composition of Example 3, according to the invention, wasprepared having the following composition:

-   -   h) 30 parts per weight D 7900 clear resin;    -   i) 60 parts per weight of a pigment dispersion P1;    -   j) 0.83 parts by weight Joncryl™ 587;    -   k) 0.41 parts by weight of TONE™ 200;    -   l) 0.0002 parts by weight dibutyltindilaurate;    -   m) 0.4 parts by weight HMDI;    -   n) 0.46 parts by weight Desmophen A450M PA/X    -   o) 0.00035 parts by weight Zinc napthenate    -   p) 0.000029 parts by weight Dimethly polysiloxane    -   q) 5.7 parts by weight CGS 80.

The ink composition of Example 4, according to the invention, wasprepared similar as the ink composition of Example 3 but using pigmentdispersion P2 to achieve a differently colored ink.

Example A 1. Screen-Printing Step

A sheet of a clear polycarbonate Makrofol™ (available from Bayer AG,Germany) with a thickness of 200 μm was screen-printed, using acommercially available flat-bed screen-printer. The desired design wasachieved by screen-printing in two steps using the ink compositions ofExamples 1 and 2.

The printed sample was dried in a flat bed oven having four stations.This drying step was done after each color printing. The samples passedthrough the heating zones at a line speed of 5.5 m per minute. Totaloven length was about 5.5 m. Temperature of the four heating zones wereas follows: zone 1: 50° C., zone 2: 60° C., zones 3 and 4 roomtemperature ventilation, maximum temperature 35° C. After the secondprinting and drying cycle the obtained printed sample was cured at 60°C. for 2 h. The dried ink coating had a thickness of ca. 6 to 10 μm.

2. Thermoforming Step

The printed sheet as obtained above was applied to a Cannon vacuumthermoformer model number Forma™ 1200 (Corso Novara 179—27029 Vigevano(PV)—Italy), in such a way that the printed area was facing the malemold. The male mold was the downside part of the thermoformingequipment. When the sheet became flexible, the vacuum led to a wrap-upof the sheet around the outside of a male mold. The temperature of thepolycarbonate's thermoforming process was around 145° C. (following ISO360 method B50).

The thermoformed sample was then separated from the mold. The final formof the sample was achieved by cutting.

3. Testing

The resulting multicoloured polycarbonate part was visually inspectedfor cracks in the printed ink layer. No cracks were found in the printedimage.

Comparative Example

Example A was repeated with the exception that an alternative ink, curedby another method, was employed. This ink was UV curable ink Dirasol™916/917 commercially available from SERICOL (Fujifilm Sericol UKLimited, Broadstairs, Kent CT10 2LE). The ink was applied as above andcured using UV lamps as recommended by the manufacturer.

The multicoloured polycarbonate part bearing the UV cured ink wasvisually inspected for cracking in the printed image. The image showedaesthetically unpleasing cracks in the ink layer that detracted from itsappearance.

Materials for the Ink Compositions of Examples 5 to 9

1903: 3M™ Screen Printing Ink 1903 White, available from 3M Company (St.Paul, Minn., USA).

3000: Silberline SPARKLE SILVER® 3000-AR (SBR) Aluminum Pigment Pasteavailable from Silberline, Inc. (Tamaqua, Pa., USA).

3122: Silberline SPARKLE SILVER® 3122-AR (SBR) Aluminum Pigment Pasteavailable from Silberline, Inc. (Tamaqua, Pa., USA).

7900: 3M™ High™ Performance Ink, 7900, available from 3M Company (St.Paul, Minn., USA).

7922: 3M™ High™ Performance blue ink, 7922, available from 3M Company(St. Paul, Minn., USA).

7937: 3M™ High™ Performance yellow ink, 7937, available from 3M Company(St. Paul, Minn., USA).

CAPA® 2054: polycaprolactone diol, Solvay Caprolactones (Warrington,Cheshire WA4 6HB, United Kingdom).

CAPA® 3050: polycaprolactone, Solvay Caprolactones (Warrington,Cheshire, United Kingdom).

DBTDL: Dibutyltin dilaurate catalyst for polymerizing isocyanatereactions, available from PolySciences, Inc. (Warrington, Pa., USA).

Xylene solvent available from Shell Chemical Company (Houston, Tex.,USA).

N-100: DESMODUR N 100 aliphatic polyisocyanate resin based onhexamethylene diisocyanate (HMDI) available from Bayer Material ScienceLLC (Pittsburgh, Pa., USA).

Tone™ 240: polycaprolactone diol, Dow Chemical Company (Midland, Mich.,USA).

HMDI: hexamethylene di-isocyanate, Desmodur™ N 3390 BA/SN, commerciallyavailable from Bayer (Bayer Material Science AG, 51368 Leverkusen,Germany).

Each ink formulation of Examples 5 to 9 was made by mixing thecorresponding components together as specified in Table 1. Each Examplecomposition was thinned to approximately 2000 cps with diethyleneglycolmonoethyl ether acetate solvent, available from Eastman Chemical Company(Kingsport, Tenn., USA). Then each formulation was silk screen printedonto 1000 micron thick Makrofol® 2099UV polycarbonate sheets, availablefrom Bayer AG (Darmstadt, Germany). The ink was printed in a checkerboard pattern of 25 mm×25 mm squares. After printing, the sheets weredried in a forced air oven at 85° C. for 30 minutes. The sheets werethen thermoformed as described above.

The percent elongation each sample experienced during thermoforming wascalculated by measuring the change in length of each side of the squaresafter thermoforming. Percent elongation is defined as (newdimension/original dimension×100). Screen printed squares that mostclosely represented percent elongations of 120%, 140%, 160% and 180%were examined and the stress effects on each examined printed ink squareafter elongation (i.e., their appearance) was rated. The samples wereexamined for the following changes in ink appearance: color change,pinholes and cracking. The change in appearance of the squares was ratedusing a 9, 3, 1 and 0 rating system. Squares with very little or nochange in appearance after thermoforming were rated a 9. Squares withsome acceptable change (i.e., limited color change, limited pinholes,and no visible cracking) in appearance after thermoforming were rated a3. Ink squares with unacceptable changes in appearance afterthermoforming (i.e., noticeable color change, large pin holes and novisible cracking) were rated a 1. Ink squares that exhibited visiblecracking after thermoforming were rated a 0. The results are shown inthe Table 1 below.

TABLE 1 Examples (amounts are parts by weight) 5 6 7 8 9 Components 790076.00 76.00 76.00 — 20.00 7922 16.00 16.00 16.00 — — 7937 — — — — 803122 5.00 5.00 5.00 — — 3000 3.00 3.00 3.00 — — 1903 — — — 100 — DBTDL,10% in xylene 0.05 0.05 0.05 0.05 0.05 Tone ™ 240 — — 5.00 5 34.19CAPA ® 2054 5.00 — — — — CAPA ® 3050 — 5.00 — — — Admix 770 — — — — —N-75 — — — — — HMDI 1.08 5.97 1.00 1 — N-100 — — — — 6.38 ElongationPerformance   120% 3 9 9 3 3   140% 1 3 3 3 3   160% 0 3 1 1 3 >180% 0 31 1 1

1. A method for forming an article having a decorative surfacecomprising: a) screen printing an ink composition comprising a curablecomposition onto at least one major surface of a thermoformablepolymeric sheet; b) curing said curable composition to obtain a printedsheet having on at least one major surface an ink comprising a curedcomposition; and c) thermoforming the printed sheet to obtain adecorated article, wherein said curable composition comprises apolyisocyanate and a component comprising isocyanate reactive groups andwherein said ink composition contains a solvent or solvent blend inwhich said curable composition is soluble.
 2. The method according toclaim 1, wherein said component having reactive groups comprises anacrylic polymer having hydroxyl groups.
 3. The method according to claim1, wherein said polyisocyanate comprises a di-isocyanate ortri-isocyanate.
 4. The method according to claim 1, wherein said solventis selected from ketones, esters, amides, or mixtures thereof.
 5. Themethod according to claim 5, wherein the solvent is selected fromcyclohexanone, isophorone, diacetone alcohol, N-methylpyrrolidone,methoxypropyl acetate, isopropoxyethyl acetate, ethoxyethyl propionate,ethyl lactate, and mixtures thereof.
 6. The method according to claim 1,wherein the curable ink material further comprises a caprolactone orpolycaprolactone compound, optionally having two or more hydroxylgroups.
 7. The method according to claim 1, wherein said thermoformablepolymeric sheet is made of a material selected from the group comprisingpolycarbonate, polyethyleneterephthalate glycol (PETG), acrylonitrilebutadiene styrene (ABS), thermoplastic polyolefin (TPO), polypropylene,acrylic compounds and mixtures thereof.
 8. The method according to claim1, wherein said thermoformable polymeric sheet is polycarbonate.
 9. Themethod according to claim 1, wherein said curing step b) comprisesheating of said printed sheet.
 10. The method according to claim 1,wherein said method includes the step of allowing the ink composition topartially penetrate into the thermoformable polymeric sheet.
 11. Articlehaving a decorative surface obtainable with the method of claim
 6. 12.The method according to claim 2, wherein said polyisocyanate comprises adiisocyanate or tri-isocyanate.
 13. The method according to claim 2,wherein said solvent is selected from ketones, esters, amides, ormixtures thereof.
 14. The method according to claim 3, wherein saidsolvent is selected from ketones, esters, amides, or mixtures thereof.15. The method according to claim 12, wherein said solvent is selectedfrom ketones, esters, amides, or mixtures thereof.
 16. The methodaccording to claim 2, wherein the curable ink material further comprisesa caprolactone or polycaprolactone compound, optionally having two ormore hydroxyl groups.
 17. The method according to claim 12, wherein thecurable ink material further comprises a caprolactone orpolycaprolactone compound, optionally having two or more hydroxylgroups.
 18. The method according to claim 13, wherein the curable inkmaterial further comprises a caprolactone or polycaprolactone compound,optionally having two or more hydroxyl groups.
 19. The method accordingto claim 14, wherein the curable ink material further comprises acaprolactone or polycaprolactone compound, optionally having two or morehydroxyl groups.
 20. The method according to claim 15, wherein thecurable ink material further comprises a caprolactone orpolycaprolactone compound, optionally having two or more hydroxylgroups.